Using a formulation of the Hartree-Fock formalism with the potential morphing method in the effective mass approximation, we calculate the effective band gap of Si nanocrystals embedded in SiO2 matrix without the existence of polysilane, as a function of their diameter in the size range 1–3.5 nm. Our results are in better agreement with the experimental data, in comparison with other existing theoretical data. For diameter smaller than 2 nm our results have the same tendency with the existing theoretical results, e.g., the discrepancy between theory and experiment seems to be essential.

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